The present invention relates to rotary electric machines and more particularly, but not exclusively, to synchronous motors.
European patent application No. EP-A-0 872 943 discloses a rotary electric machine in which the rotor has magnets placed on its surface and the magnetic circuit of the stator receives individual coils. The stator exerts diametrically opposite rotating radial forces on the rotor. This causes the stator to be subjected to mechanical stress tending to ovalize it, thus generating vibration and noise. Finally, the width of the teeth is constant which gives rise to at least two drawbacks: firstly the magnetic material of the stator can become saturated at the roots of the teeth; and secondly replacing a coil requires the stator to be re-impregnated, so as to lock the coil properly in place on the stator, which means that the machine cannot be repaired on site and must be returned to the manufacturer.
In particular, the invention makes it easier to manufacture stators with windings on teeth, i.e. in which each tooth constitutes the core of a winding. In a stator with windings on teeth, the number of teeth nteeth is preferably a function of the number of pairs of poles npairs and the number of phases nphases in compliance with the relationship nteeth=npairs*nphases.
The invention achieves this by means of a novel rotary electric machine stator comprising a stator magnetic circuit having teeth and individual coils each engaged on a tooth, each coil including connection ends formed by respective flat bundles of stripped wires curved to form respective hook shapes, said connection ends being soldered to locally stripped portions of sheathed electric cables.
The use of individual coils as defined above, in combination with sheathed electric cables, makes the machine easier to build and maintain. In particular, a coil can easily be replaced without having to return the machine to the manufacturer, thereby making it possible to reduce the period of time in which the installation associated with the machine is out of service.
The above-mentioned hooks can be directed towards the midplane of the coil perpendicular to the winding axis of the coil, thereby enabling the machine to be more compact.
In a particular embodiment, each tooth presents two substantially plane and non-parallel opposite faces which converge at an angle towards the rotor, and each coil presents an inside section having two opposite faces forming an angle that is substantially equal to that of the teeth, in such a manner as to be able to be wedged thereon.
This clamping effect is particularly useful in contributing to ensuring that a pre-impregnated replacement coil does not move once it has been mounted on the stator, without it being necessary to reimpregnate the entire stator in an insulating resin. Such a clamping effect is not possible with the machine described in patent application EP-A-0 872 943 in which the teeth are of constant width. In addition, another advantage of having teeth of width that increases starting at a certain distance from their free ends going away from the rotor lies in the greater section offered to the magnetic field lines reducing the risk of the magnetic laminations becoming saturated. This makes it possible to use a magnetic material that is less expensive.
In a particular embodiment, each individual coil comprises a bundle of insulated wires, the bundle being substantially flat and wound around a winding axis in such a manner as to form a plurality of superposed turns, the cross-section of the bundle in the superposed turns having a long dimension that extends substantially perpendicularly to the winding axis of the coil. The wires are preferably circular in section, having a diameter that lies in the range 0.3 millimeters (mm) to 2.5 mm, for example. This configuration makes it possible to reduce high frequency losses within the copper at high speeds of rotation of the rotor.
In such a coil, the turns can be touching, thereby ensuring that the slots are well filled.
The inside section of the coil is preferably substantially rectangular. Advantageously it is wider on one side than on the other so as to allow it to be mounted on a tooth of complementary profile with a certain amount of clamping, as mentioned above.
In a particular embodiment, the teeth of the stator include cutouts enabling support shims of the individual coils mounted on the teeth to be fixed on the stator, each shim including a separating partition extending substantially to the middle of the corresponding slot.
Each coil advantageously presents an inside section whose long side is longer than the axial size of the tooth on which it is engaged so as to leave a gap that is large enough to pass a detector that serves to deliver a signal representative of the rotation of the rotor. The machine advantageously includes at least one magnetic field detector mounted on the stator in such a manner as to detect the magnetic field of the rotor magnets from a location that overlaps a peripheral region of the rotor when the machine is observed on the axis of rotation of the rotor. This peripheral region is advantageously the region which extends around an end cheek-plate situated so as to be set back from the radially outer edge of the magnets.
For n-phase AC, the machine preferably has n detectors mounted on n consecutive teeth close to an opening through a case of the machine. Such a detector or detectors can be fixed on a face of the magnetic circuit of the stator and each can extend along the radial axis of the corresponding tooth. Advantageously each detector passes through the coil engaged on the corresponding tooth, as mentioned above. This enables the machine to be more compact.
The invention also provides a synchronous motor comprising a permanent magnet rotor, preferably a flux-concentrating rotor, and a stator with windings on teeth as defined above.
The combination of a flux-concentrating rotor and a stator with windings on teeth makes it possible to have a machine that is relatively powerful in a small volume, thus making it possible in particular to mount the motor in a cantilevered-out position at the end of a shaft, thereby reducing the number of bearings.
Such a structure also enables the cost of the machine to be reduced since the number of teeth and the number of coils is relatively small.
In addition, the stator is compact since the heads of the coils are short.
The phases can be separated electrically without contact and without crossovers.
The invention also provides a method of manufacturing a stator, the method comprising the following steps:
manufacturing a stator magnetic circuit having teeth;
manufacturing individual coils each having electrical connection ends formed by respective flat bundles of stripped wires curved to form respective hook shapes; and
soldering the electrical connection ends of the coils to sheathed cables that are partially stripped at the connection points with the coils.